The influence of maternal size on placental, fetal and postnatal growth in the horse. II. Endocrinology of pregnancy

Abstract

Within-breed artificial insemination and between-breed embryo transfer were carried out in small pony (P) and large Thoroughbred (Tb) mares to create 4 types of horse pregnancy in which the fetus experienced spatial and nutritional deprivation (Tb-in-P; n=8), luxury (P-in-Tb; n=7) or normality (Tb-in-Tb; n=7 and P-in-P; n=7) in utero.Measurement of equine chorionic gonadotrophin (eCG), total conjugated oestrogens and progestagen concentrations in serial peripheral serum samples recovered from all the mares throughout gestation showed that the amount of eCG produced during the first half of gestation was dependent upon the breed of the mare rather than the breed of the fetus being carried. In contrast, the mean total amounts of oestrogens produced, as measured by area under the curve, were significantly greater (P=0·003) in the two types of pregnancy in which a Thoroughbred fetus was being carried (Tb-in-Tb and Tb-in-P) than those in which a pony fetus was gestated (P-in-P and P-in-Tb); the evidence suggests that the Tb fetus may have larger gonads than the P fetus and thereby secrete more C-19 precursor steroids for aromatisation to oestrogens by the placenta. In the final weeks of pregnancy mean plasma progestagen concentrations rose much earlier, and to significantly higher levels (P<0·001), in the Tb-in-P than in the P-in-Tb pregnancies, thereby reflecting the increased fetal stress in the former causing premature maturation of the fetal adrenal gland. This, in turn, resulted in increased secretion of pregnenolone by the adrenal cortex for conversion to progestagens by the placenta.

Factors affecting gestational length in the Mangalarga Paulista breed

“…In the literature, gestational length has been reported for Thoroughbred (Allen et al, 2002;Davies Morel et al, 2002;Duggan et al, 2008;Elliott et al, 2009), American Quarter Horse (QH; Duggan et al, 2008), Criollo (Winter et al, 2007), Pantaneiro Horse (Zuccari et al, 2002), Lusitano (Pérez et al, 2003;Valera et al, 2006) and Arabian (Valera et al, 2006) mares. In all of these studies, the mean gestational length ranged between 330 and 350 days (Satué et al, 2011a).…”

Avaliação hormonal sérica e estereológica da membrana corioalantóide a termo de éguas: influência no desenvolvimento e nos parâmetros clínicos e metabólicos do potro

“…Trata-se de um hormônio glicoproteico de alto peso molecular secretado pelas células do cálice endometrial, que expressa aproximadamente em igual proporção hormônios com atividade biológica tipo FSH e LH (STEWART; ALLEN; MOOR, 1976;ALLEN et al, 2002b).…”

“…Os níveis circulantes de eCG podem ser detectados pela primeira vez entre os dias 37 a 41 após a ovulação, e aumentam rapidamente até alcançar um pico sérico aos 55 -75 dias, declinando à concentrações muito baixas ou indetectáveis a partir dos 120 dias de gestação (ALLEN, 1969;ALLEN, 1975), refletindo o ciclo de desenvolvimento e degeneração dos cálices endometriais (ALLEN et al, 2002b (BARNES et al, 1975;RAESIDE et al, 1979. TERQUI;PALMER, 1979).…”

“…Provavelmente o estresse fetal estimulou o aumento da produção de P 5 pelo feto e consequentemente as concentrações séricas de metabólitos da progesterona no sangue materno (ALLEN et al, 2002b).…”

“…Muitos aspectos da secreção de hormônios esteróides pela unidade feto-placentária em éguas são exclusivos para esta espécie e de especial interesse científico (ALLEN et al, 2002b). Trata-se de um processo dinâmico que compreende desde a concepção até o parto e este período de vida intrauterino é necessário para garantir o desenvolvimento fetal e a capacidade de sobrevivência ao meio externo .…”